The present disclosure relates to an interior permanent magnet type rotor, a permanent magnet type motor having the interior permanent magnet type rotor, and a compressor having the permanent magnet type motor.
Since a permanent magnet type motor uses a permanent magnet instead of a coil for a rotor, it is unnecessary to supply power to the coil. Thus, the permanent magnet type motor has high efficiency, and its maintenance cost is reduced as its operation time becomes longer. Accordingly, the permanent magnet type motor has recently come into the spotlight.
The permanent magnet type motor may be classified into an interior permanent magnet type motor and a surface permanent magnet type motor.
The interior permanent magnet type motor is a motor of a type in which a permanent magnet is embedded in a rotor, and the surface permanent magnet type motor is a motor of a type in which a permanent magnet is attached to an outer circumferential surface of a rotor.
As a design for increasing a motor speed is performed so as to design a high-output and high-efficiency motor having a small size, the surface permanent magnet type motor has recently been replaced by the interior permanent magnet type motor.
The interior permanent magnet type motor has the following advantages as compared with the surface permanent magnet type motor.
First, since a permanent magnet is embedded in a rotor core, an adhesive force of the permanent magnet, which overcomes a centrifugal force and a maximum torque, can be guaranteed. Thus, the interior permanent magnet type motor is strong and advantageous in high-speed rotation.
Second, a magnetic torque and a reluctance torque are available together, and thus a high torque can be realized.
Third, the external diameter of a rotor is elaborately processed, and thus a gap can be reduced.
Fourth, the loss of eddy current on a rotor surface is reduced, and thus high efficiency can be realized.
Fifth, the range of operating speed can theoretically approach to infinity through weak field control, and thus the interior permanent magnet type motor is advantageous in high-speed rotation.
However, as compared with the surface permanent magnet type motor, the interior permanent magnet type motor using the reluctance has a large cogging torque due to characteristics of the rotor, and therefore, a large noise is generated in an operation of the interior permanent magnet type motor.
In particular, when the permanent magnet embedded in the rotor has a shape symmetrical with respect to a vertical axis or a horizontal axis, e.g., a rectangular shape, the interior permanent magnet type motor has a cogging torque larger than that of a motor in which a skewed magnet is embedded, and therefore, a large noise is generated.
In order to solve such a problem, there has been proposed a motor in which a skewed magnet inclined in a parallelogram shape is applied to a rotor core (see Prior Art).
However, the prior art has a problem as follows.
In detail, a slot into which a magnet is inserted has a rectangular shape that is symmetric laterally and vertically, and the magnet inserted into the slot has a skewed shape, i.e., a parallelogram shape.
Therefore, after the magnet is inserted into the slot, there occurs a phenomenon that the magnet vibrates or shakes in the slot. In order to prevent such a vibration or shaking phenomenon, when a skewed main magnet is inserted in a slot, a sub-magnet for filling in a gap is inserted into the slot together with the skewed main magnet such that the slot is completely filled. Therefore, the manufacturing cost of the motor increases, and the manufacturing process of the motor is complicated.
Prior Art: Japanese Patent Laid-open Publication No. 1988-174324 (Jun. 26, 1998)